This invention relates to latching apparatus for use with first and second adjacent doors each adapted for independent movement between open and closed positions. Doors with which the latching apparatus is particularly adapted for use are so-called French doors usually located either at the front or rear entrance of a home or other building and adapted to be swung between their open and closed positions.
In a double door system of this type, one of the doors typically is referred to as an active door since that door is the one which is most frequently opened to permit passage to and from the home. The other door is conventionally called a passive door. It usually is opened only when large furnishings or the like are moved into and out of the home or when it is desired to provide maximum ventilation or maximum visual exposure through the doors.
In some installations, the passive door is adapted to be held releasably in its closed position by upper and lower latch elements which coact with the top header and the lower sill of the door frame. A latch operating mechanism is associated with the passive door and may be manually actuated from inside the home to withdraw the latch elements from the header and sill and permit opening of the passive door.
The active door is adapted to be held in its closed position by one or more latch elements which latch into an astragal on the upright free edge of the passive door. In one type of active door, the latch elements comprise upper and lower hook latches, a center spring latch and a center deadbolt. The active door is adapted to be locked by throwing the deadbolt either with a turn knob from inside of the home or with a key-operated mechanism from the outside.
Because the active door is latched and locked only to the astragal of the passive door, the security of the door system is dependent upon the security with which the passive door is latched. If the passive door is left unlatched, an intruder may more easily gain access to the home even though the active door is latched and locked to the passive door. Also, strong winds can damage the door system due to the fact that the passive door is not latched to the header and sill of the door frame.
In an effort to overcome the problem of the passive door being left unlatched when the active door is locked, it has been proposed to provide a latching system which prevents the active door from being locked if the passive door is closed but unlatched. With this arrangement, the homeowner--upon attempting and failing to lock the active door--is warned that the passive door is unlatched and must take steps to latch that door before he/she can lock the active door. Such an arrangement does not, however, prevent the homeowner from unlatching and attempting to open the passive door while the active door is either latched or latched and locked to the astragal of the passive door. If such an attempt is made, damage can result to the locking system and/or the doors.